Buildings and Cities

Landfill Methane

Wellhead for methane capture at a landfill in Michigan.

Over the course of a century, methane has 34 times the greenhouse effect of carbon dioxide. Landfills are a top source of methane emissions, releasing 12 percent of the world’s total. Landfill methane can be tapped, captured, and used as a fairly clean energy source for generating electricity or heat, rather than leaking into the air or being dispersed as waste. The climate benefit is twofold: prevent landfill emissions and displace coal, oil, or natural gas that might otherwise be used.

Most landfill content is organic matter: food scraps, yard trimmings, junk wood, wastepaper. Their decomposition produces biogas, a roughly equal blend of carbon dioxide and methane accompanied by a smattering of other gases. Ideally, those wastes would be recycled, composted, or digested. But as long as landfills are piling up, we must manage the methane coming out of them.

The technology to manage biogas is relatively simple. Dispersed, perforated tubes are sent down into a landfill’s depths to collect gas, which is piped to a central collection area where it can be vented or flared. Better still, it can be compressed and purified for use as fuel in generators, garbage trucks, or mixed into natural gas supply.

#58

Rank and Results by 2050

2.5 gigatonsreduced CO2

$-1.82 Billionnet implementation cost

$67.57 Billionnet operational savings

Impact: This solution sits at the bottom of the waste hierarchy. Landfill waste will decline as diets change, waste is reduced, and recycling and composting grow. What cannot, or should not, be combusted in waste-to-energy facilities will reach landfills as a last resort. These solutions will not be adopted globally overnight, so we assume landfill methane capture will continue to play a role. Combusting landfill methane for electricity production can result in emissions reductions equivalent to 2.5 gigatons of carbon dioxide.

Landfill methane capture is most effective in closed and engineered landfills, achieving 85 percent efficiency or more; it is least effective in open dumps, where the collection efficiency is approximately 10 percent and capture is typically not seen as an economically favorable decision. As a waste treatment solution, from a climate perspective, landfill methane is generally seen as preferable only to landfilling without methane capture. However, where landfills exist it is an important solution for mitigating greenhouse gases.

Methodology

This analysis models the impacts of the adoption of landfill methane for electricity generation and gas flaring. Landfill methane is a mature technology which has been used widely for decades.

The total addressable market for landfill methane is based on projected global electricity generation in terawatt-hours from 2020-2050. Current adoption [2] is considered to be 23.99 terawatt-hours, or 0.11 percent of total electricity generated worldwide (IRENA, 2016). Total adoption estimates vary widely between different future adoption prognostications, due to the fact that different sources place a different value on biomass and waste for energy adoption.

Impacts of increased adoption of landfill methane from 2020-2050 were generated based on three growth scenarios derived from the evaluation of several global energy system modeling scenarios. These scenarios were assessed in comparison to a Reference Scenario where the solution’s market share was fixed at the current levels.

The sources used do not clearly depict landfill methane and biogas technologies for electricity generation adoption pathways; instead, their results combine biomass and waste for electricity generation. Therefore, a few assumptions were made to determine future adoption: biogas represents around 20 percent of total electricity generation from bioenergy worldwide, and biogas from landfills covered within this solution represents 30 percent of total biogas. The remaining 70 percent is covered by methane capture from agriculture, manure, and wastewater.

For landfill methane, three scenarios were developed:

Plausible Scenario: Due to landfill methane’s low priority in waste management ranking, the Plausible Scenario is built upon three reference scenarios from the EU project AMPERE (2014), [4] and the 6°C Scenario of the International Energy Agency’s 2016 Energy Technology Perspectives (IEA ETP, 2016). Using a medium growth trajectory, the Plausible Scenario foresees landfill methane capture reaching 0.26 percent of the market share in 2050.

Drawdown Scenario: The Drawdown Scenario follows the adoption projected by the AMPERE MESSAGE-Macro model in the 450 scenario, reaching a market share in 2050 of 0.09 percent.

Optimum Scenario: The Optimum Scenario depicts 0.08 percent of the total electricity generation in 2050, after the trajectory proposed by the Greenpeace Advanced Energy [R]evolution Scenario. [5]

Emissions Model

Landfill methane emission rates are estimated using the first-order decay method recommended by the Intergovernmental Panel on Climate Change (IPCC), in order to estimate both total emissions reductions for landfill gas-to-electricity generation and an increase in landfill gas flaring.

Financial Model

The financial inputs used in the model assume installation costs of US$1,723 per kilowatt (IRENA, 2012; EESI, 2013; US EPA, OAR, 2016). [6] Inputs were determined from the variable meta-analysis done, and account for the extra costs of flaring systems. Due to the maturity of landfill methane technology, a learning rate of 2 percent was applied. An average capacity factor of 80 percent was used for the solution, compared to 55 percent for conventional technologies. An average fixed operation and maintenance cost of US$212.7 per kilowatt was used in the calculations, compared to US$33.0 per kilowatt for the conventional technologies.

Through the process of integrating landfill methane with other solutions, the total addressable market for electricity generation technologies was adjusted to account for reduced demand resulting from the growth of more energy-efficient technologies, [8] as well as increased electrification from other solutions like electric vehicles and high-speed rail. Grid emissions factors were calculated based on the annual mix of different electricity-generating technologies over time. Emissions factors for each technology were determined through a meta-analysis of multiple sources, accounting for direct and indirect emissions.

Results

The results for the Plausible Scenario show that through the advanced adoption of landfill methane, installed in over 70 percent of the world’s landfills, the net first costs compared to the Reference Scenario would be US$1.82 billion in savings from 2020-50 and approximately US$67.57 billion in operational savings over the same period. Increasing the use of landfill methane from 0.11 percent in 2014 to 0.26 percent of world electricity generation by 2050 would require an estimated US$35.30 billion in cumulative first costs. Under the Plausible Scenario, landfill methane’s increased use could reduce 2.5 gigatons of carbon dioxide-equivalent greenhouse gas emissions from 2020-2050.

Both the Drawdown and Optimum Scenarios are more conservative in the growth of landfill methane due to the combination with other waste management solutions, with impacts on greenhouse gas emission reductions over 2020-2050 of 1.11 and 0.5 gigatons of carbon dioxide-equivalent, respectively.

Discussion

Landfill methane solutions are a net benefit for the climate. From a financial perspective, while some up-front costs are required for landfill gas-to-electricity technologies, the long-term return on investment is significant, and therefore these technologies are a sound investment.

While it is clearly a ‘second-best’ waste management strategy, as long as landfills are being created it is still a viable and important solution for climate mitigation. Aside from the significant climate benefits and long-term cost savings shown by this study, landfills which capture methane are safer and less of a public health hazard than those which do not. Therefore, as landfills move globally from open dumps or basic landfills to engineered sanitary landfills, the percentage of landfills which use landfill methane capture can and should be expected to increase.

[1] For more about the Total Addressable Market for the Energy Sector, click the Sector Summary: Energy link below.

[2] Current adoption is defined as the amount of functional demand supplied by the solution in the base year of study. This study uses 2014 as the base year due to the availability of global adoption data for all Project Drawdown solutions evaluated.